The field of tribology concerns the study of friction and wear between material surfaces in contact and under relative sliding motion. Thus, the field of tribology involves measurement and calculation of such parameters as friction and wear rate of materials such as used in the construction of mechanical parts. Knowledge of these parameters is useful for the study of the behavior of the same or different materials in moving contact in order to evaluate materials to be used in the construction of mechanical parts and to estimate the potential for failure of those parts over time.
Tribotesting apparatus has previously been developed to test the wear characteristics of material samples. The traditional tribotester is referred to the "pin-on-disk" tester wherein a sample of material is placed on a turntable that may be rotatably driven. A contact element may be subjected to different loading forces so that it bears normally downwardly on the sample of material and, as the sample of material rotates on the turntable, a single wear band is traced in a circle around the material sample. The point of the contact element may be formed of the same material as the sample or a different material, as desired. An added feature of rotating the sample while radially oscillating the contact element may be employed by a tribotester thereby to cause the contact element to trace a spiral line across the surface of the sample. Accordingly, a wear path in the shape of a race track would be formed on the sample with this race track having a width equal to the radial distance over which the contact element is reciprocated. In the abovedescribed cases, the tribotesting apparatus was designed to operate under normal ambient environment conditions.
Knowing the wear characteristics of materials under normal ambient conditions is quite useful since many applications of materials are in situations of normal ambient atmosphere such as is found on the surface of the earth. However, an increasing number of applications are in conditions other than the normal ambient environmental conditions. One such example would be found in the semi-conductor industry wherein a substantial portion of processing is done in atmospheres that are rich in corrosive gases.
Another area where conditions are significantly different from earth surface normal is in the aeronautics and space industry. For example, in high altitude and earth orbit that the atmosphere is greatly rarefied, and a significant problem manifests in the presence of atomic oxygen, a highly corrosive gas that which readily attacks many lubricious materials. Thus, the surfaces of mechanical parts which are designed for relative movement with reduced friction rapidly become degraded and may fail. The search for materials resistive to atomic oxygen goes on in an effort to locate materials less susceptible to failure due to the corrosive nature of atomic oxygen in these environments. Other examples in the space industry, of course, are the atmospheres of different planets.
Yet another example of an environment of increasing interest is the undersea environment wherein the corrosive action of salt water may also act to degrade materials employed in underwater equipment. Propeller shafts are known to fail in their bearings as a result of the degradation from the corrosive nature of sea water; likewise, oil drilling and undersea mining applications employ machines susceptible to such degradation.
Accordingly, a need exists for methods and apparatus to test the wear characteristics of materials in environments different than the ambient environment at the surface of the earth. The need exists for such testing equipment which may be used to test materials in a fluid environment that may be in the liquid phase or gaseous phase. The present invention addresses these needs.